Zika virus remained in relative obscurity for many years, but within a period of just 1 year, it has spread into Brazil, Pacific Island, and throughout the Americas. Zika virus disease has become the fetal infectious disease which is associated with human birth defects and created such global havoc that the World Health Organization declared a public health emergency of international concern. This review summarizes the transmission, distribution, clinical features, diagnosis, prevention, and future perspectives of Zika virus disease.

A new virus was first discovered in 1947 from the blood of a sentinel rhesus macaque that has been placed in Zika forest in Uganda while doing a study of yellow fever and thus, the new virus is named after the Zika forest as "Zika virus." [1] The structure of Zika virus is shown in [Figure 1]. Zika virus disease is an emerging mosquito-borne virus and it is transmitted primarily by Aedes aegypti mosquitoes which usually bite during the day with peaks during early and late afternoon/evening hours. [2]

Mainly, it spreads by the bite of an infected mosquito A. aegypti from Aedes genus. Sexual transmission can occur from a man to his sex partners. Blood transmission and perinatal transmission can also be possible. They are currently being investigated. [2],[3]

Distribution

Zika virus was first identified in Uganda in 1947 in rhesus monkeys through a monitoring network of sylvatic yellow fever. It was subsequently identified in humans in 1952 in Uganda and the United Republic of Tanzania. Outbreaks of Zika virus disease have been recorded in Africa, the Americas, Asia, and the Pacific. Zika virus outbreaks have probably occurred in many locations. Distribution of Zika virus disease is shown in [Table 1]. [4],[5]

Mostly, people with Zika virus disease have no symptoms but if they are present, they are usually mild and last for 2-7 days. Incubation period of Zika virus is believed to be few days. Symptoms are similar to other arbovirus infections such as dengue. They are mentioned as follows [Figure 2]: [2],[6],[7]

Zika virus infections in adults have been linked with Guillain-Barre syndrome, which is a rapid onset of muscle weakness caused by the immune system damaging the peripheral nervous system, which can progress to paralysis. [2],[6],[7]

Diagnosis

Diagnosis is done by testing the blood, urine, or saliva for the presence of Zika virus RNA when the person is sick. [2],[6] Zika virus can be identified by reverse transcriptase polymerase chain reaction (RT-PCR) in acutely ill patients. However, the span of viremia can be short. [8] The World Health Organization recommends that RT-PCR testing should be done on the collected serum within 1-3 days of symptom onset or on saliva or urine samples collected during the first 3-5 days. Zika virus was detected more frequently in saliva than serum when evaluating paired samples. [9] The longest period of detectable virus has been 11 days and Zika virus does not appear to establish latency. Furthermore, serology for the detection of specific IgM and IgG antibodies to Zika virus can be used. IgM antibodies can be detectable within 3 days of the onset of illness. [10] Serological cross-reactions with closely related flaviviruses such as dengue and West Nile virus as well as vaccines to flaviviruses are possible. [8],[11],[12]

Screening during pregnancy

The Centers for Disease Control and Prevention (CDC) recommends screening of pregnant women even if they do not have symptoms of infection. Pregnant women who have traveled to affected areas should be tested between 2 and 12 weeks after their return from travel. For women living in affected areas, the CDC has recommended testing at the first prenatal visit with a doctor as well as in the mid-second trimester, though this may be adjusted based on local resources and the local burden of Zika virus. Additional testing should be done if there are any signs of Zika virus disease. Women with positive test results for Zika virus infection should have their fetus monitored by ultrasound for every 3-4 weeks to monitor fetal anatomy and growth. [13]

Infant testing

For infants with suspected congenital Zika virus disease, the CDC recommends testing with both serologic and molecular assays such as RT-PCR, IgM ELISA, and plaque reduction neutralization test. Newborns with a mother who was potentially exposed and who had positive blood tests, microcephaly, or intracranial calcifications should be further tested including a thorough physical investigation for neurologic abnormalities, dysmorphic features, splenomegaly, hepatomegaly, and rash or other skin lesions. In addition, the recommended tests are cranial ultrasound, hearing evaluation, and eye examination. Testing should be done for any abnormalities encountered as well as for other congenital infections such as syphilis, toxoplasmosis, rubella, cytomegalovirus infection, lymphocytic choriomeningitis virus infection, and herpes simplex virus. [14]

Prevention

The virus is mainly spread by mosquitoes, so avoidance and control of mosquitoes are important elements for Zika virus disease prevention.

Measures for mosquito avoidance

Cover exposed skin by wearing long-sleeved shirts and long pants

Use an insect repellent

Stay and sleep in screened-in or air-conditioned rooms

Use a bed net if the area where you are sleeping is exposed to the outdoors.

Measures for mosquito control

Control mosquitoes such as eliminating standing water where they replicate

Repairing septic tanks

Using screens on doors and windows

Spraying insecticide which is used to kill flying mosquitoes and larvicide can be used in water containers. [15],[16]

Measures to control the spread of sexual transmission

Sexual transmission of Zika virus is possible. All people who have been infected with Zika virus and their sexual partners should practice safer sex by following the measures mentioned below:

Use condoms correctly and consistently

Pregnant women's sex partners living in or returning from areas where local transmission of Zika virus occurs should practice safer sex, wear condoms, or abstain throughout the pregnancy

People living in areas where local transmission of Zika virus occurs should practice safer sex or abstain from sexual activity

People returning from areas where local transmission of Zika virus occurs should adopt safer sexual practices or consider abstinence for at least 4 weeks after their return to reduce the risk of onward transmission. [16],[17],[18],[19]

Furthermore, an integrated prevention and vector control approach combined with timely detection of illness, communication of current and correct information, and development of a rapid response that involves the community is recommended. [20]

Treatment

Zika virus disease is usually relatively mild and requires no specific treatment. People affected by Zika virus should get plenty of rest, drink enough fluids, and treat pain and fever with common medicines. If symptoms get worsen, they should seek medical care and advice. There is currently no vaccine available.

Future Perspectives

The current outbreak of Zika virus disease is difficult to gauge because the symptoms are nonspecific and usually mild, laboratory diagnosis is not uniformly available, and cross-reactivity of flavivirus antibody complicates serologic assessment in areas in which dengue is endemic. There is a need to rapidly and systematically address the identified research gaps for controlling the disease. Future perspectives include a complete understanding of the frequency and full spectrum of clinical outcomes resulting from fetal Zika virus disease, the environmental factors that influence emergence, the development of discriminating diagnostic tools for flaviviruses, developing animal models for fetal developmental effects due to viral infection, new vector control products and strategies, effective therapeutics, and vaccines to protect humans against the disease. [21]